A big warning before we send you out into the freezing cold with a bucketful of boiling water: This is an experiment that isn't just dangerous for kids but adults, too. Be very vigilant about things like wind direction and speed -- not to mention cautious about boiling water, period.
But if you're all bundled up and taking proper precautions, this experiment is a likely candidate to impress even the most jaded youngster. The theory is this: Because hot liquid evaporates faster than cold, throwing some boiling water into cold air will create instant snow. The cold air can't accommodate all the water vapor you're throwing at it and combines with tiny airborne particles to form snow [source: Thompson].
It's absolutely true, but not as simple as throwing hot water on a regular old winter day. It has to be extremely cold. We're talking minus 20 degrees Fahrenheit (minus 29 degrees Celsius) here. You might be surprised at just how much snow volume results. A coffee mug will create a decent storm, and an entire bucket will make you feel like you're in a blizzard.